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    <script>
        var arr = [5, 4, 3, 2, 1];
        var num;
        for (var i = 0; i <= arr.length - 1; i++) { //外层循环管理趟数
            for (var j = 0; j <= arr.length - i - 1; j++) { //内层循环管理每一趟交换次数
                if (arr[j] > arr[j + 1]) { //前一个和后一个数组元素相比较
                    num = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = num;
                }
            }
        }
        console.log(arr);
    </script>
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